It is well known that a conductive object that is immersed into a bath containing a metallic salt solution may acquire a metallic coat when the object constitutes a cathode in an electric circuit during current supply. A coating will be obtained in the whole surface exposed to the metallic salt solution. If it is desired to locate the coating at a smaller region, so-called brush plating is often used, whereby the electrolyte is located at a certain region with the aid of a liquid-absorbing material. Only the region that is in contact with the liquid-absorbing material will then be coated. Examples of such liquid-absorbing materials are rubber sponge and cloth of so-called Scotch-Brite®. Because of the high current densities that are used, brush plating takes place under relative movement between anode and cathode. Too slow a relative movement may cause burn-in effects on the layer, whereas too fast a relative movement may cause an unnecessarily slow rate of coating. The layer thickness obtained depends on the concentration of metal ions in the salt solution and the electric energy supplied. The electric energy supplied may, for example, be expressed as the electric current multiplied by time, for example expressed in Ah.
Brush plating is described, for example, in “Lärobok i Elektrolytisk och Kemisk Ytbehandling” (“Textbook in Electrolytic and Chemical Surface Treatment”), volume 1, published by Ytforum/G Ekström's publishing house, Linköping 1994, pp. 410-416. If different portions of the conductive object are to be coated with layers of different thickness, the coating must take place in steps where each region is coated separately. When rotationally symmetrical objects such as, for example, tubes are to be coated with layers of different thickness on different places, masking is used such that those parts that are not to be coated to layer thickness A are masked, whereas those parts which are to be coated to layer thickness A are exposed, whereupon those parts which have layer thickness A are masked and those parts which are to receive layer thickness B are exposed. For each desired layer thickness, at least one process step is added. When several different parts are to be coated with layers of different thickness, the process is complicated and time-wasting. The probability of errors increases with the number of process steps, and the costs of rejections may be considerable.